Process for preparing 2:2&#39;-dipyridyls



United States Patent 3,173,920 PROCESS FOR PREPARING 2:2'-DIPYRIDYLSGeorge Henry Lang, Manchester, England, assignor to Imperial ChemicalIndustries Limited, London, England, a corporation of Great Britain N0Drawing. Filed July 1, 1963, Ser. No. 292,109 Claims priority,application Great Britain, July 3, 1962, 25,524! 62 8 Claims. (Cl.260-496) This invention relates to a new process for the manufacture of2:2-dipyridyls from pyridine or alkyl pyridines.

2:2'-dipyridyl and certain of its alkyl derivatives are valuableintermediates for the preparation of herbicides and may be prepared bythe action of Raney nickel catalyst on pyridine or the appropriatealkylpyridine. The use of this catalyst however introduces a firehazard, and furthermore the catalyst rapidly loses activity during thereaction and is not capable of regeneration.

We have now found that rhodium, osmium or iridium act as catalysts forthe conversion of pyridine into dipyridyls and in comparison with Raneynickel exhibit greater resistance to poisoning and are less hazardous inuse.

According to our invention therefore we provide an improved process forthe manufacture of 2:2'-dipyridyl and alkyl derivatives thereof frompyridine or an alkylpyridine by heating at a temperature above 100 C.with a catalyst containing rhodium, osmium or iridium in finely dividedform.

As alkylpyridines which may be used in the process of our inventionthere may be mentioned for example any pyridine carrying a lower alkylgroup, by which is meant an alkyl group containing not more than sixcarbon atoms. Two alkyl groups may be present but the groups must not bein both the 2 and 6 positions of the pyridine ring and should notcontain altogether more than six carbon atoms. As examples of suchalkylpyridines there may be men tioned S-methyl and 4-methylpyridineswhich afford re spectively 5:5-dimethyl and4:4'-dimcthyl-2:2-dipyridyls.

The rhodium, osmium or iridium catalyst may be prepared by conventionalmethods for example as described on pages 139-141 of AnnotatedBibliography on Ruthenium, Rhodium and Iridium as Catalysts, publishedby The International Nickel Company, Inc. It is preferred that thecatalyst be supported on for example alumina, silica, animal charcoal,asbestos, pumice and kieselguhr, such supported catalyst being preparedby conventional methods such as impregnation with soluble salts followedby reduction with for example formaldehyde, hydrazine, or hydrogen. Thecatalyst may be in powder or granular form.

The amount of catalyst used influences the rate of reaction. It ispreferred to use a quantity of catalyst which, together with anysupporting material, is between -1 and 50% of the Weight of pyridine.

The preferred temperatures for carrying out the process of our inventionare between 250 and 450 C. T emperatures below this range, for examplebetween 100 and 250 C. can be used but give low speeds of conversion,and higher temperatures lead to side reactions.

The process may be carried out by heating the catalyst and pyridine tothe desired temperature in an agitated, enclosed vessel capable ofwithstanding the high pressure produced.

The optimum time of reaction varies wtih the temperature used and thepyridine. Using pyridine itself and 4% or 5% rhodium on alumina catalystlittle further reaction takes place after about 10 hours at 300 C. Afterreaction the catalyst is removed, for example, by filtration.

If desired however the process can be carried out in a continuousmanner, for example by circulation continuously over the catalyst ofunreacted pyridine recovered from the reaction mixture by distillation,the dipyridyls accumulating in a vessel separate from that containingthe catalyst. By adjustment of the pressure, the catalyst can beoperated under vapour phase or liquid phase conditions.

The catalyst can be reactivated after use by oxidative and reductivemethods or regenerated by solution of the metal for example a mixture ofnitric and hydrochloric acids followed by reductive treatment toreprecipitate the metal.

The invention is illustrated but not limited by the following examplesin which all parts and percentages are by weight unless otherwisespecified.

Example 1 1 part of catalyst consisting of 5% rhodium on alumina and 25parts of pyridine are heated in a sealed glass pres sure tube at 300 C.for 10 hours. After cooling the catalyst is removed by filtration togive a solution in pyridine of 2:2'-dipyridyl, corresponding to a rateof production of dipyridyl of 760 parts per hour per parts of rhodium.

Example 2 05 part of catalyst consisting of 5% rhodium on alumina and 25parts of 4-methylpyridine are heated in a sealed glass pressure tube at300 C. for 10 hours. On cooling, the contents become partly solid andare washed out with methanol. The suspension is heated to dissolve theorganic material and the catalyst removed by filtration. Onconcentration and cooling 4:4'-dimethyl-2:2'- dipyridyl crystallisesout. The amont obtained was 6.75 parts equivalent to a rate ofproduction of 2700 parts per hour per 100 parts of rhodium.

What I claim is:

1. An improved process for the manufacture of 2:2- dipyridyl and alkylderivatives thereof from a first member selected from the groupconsisting of pyridine and an alkylpyridine by heating said first memberat a temperature above 100 C. with catalyst containing a second memberselected from the group consisting of rhodium, osmium and iridium infinely divided form.

2. A process as claimed in claim 1 wherein the alkyl group in thealkylpyridine contains not more than six carbon atoms.

3. A process as claimed in claim 2 wherein the alkyl group is a methylgroup in the 3-position of the pyridine ring.

4. A process as claimed in claim 1 wherein the temperature is between250 and 450 C.

5. A process as claimed in claim 1 wherein said second member issupported on a substrate.

6. A process as claimed in claim 1 wherein the amount of catalyst isfrom 1 to 50% of the weight of pyridine.

7. A process as claimed in claim 1 wherein said first member is broughtinto contact with the catalyst, removed from the catalyst with furtheramounts of said first member, separated by distillation from a thirdmember 7 3 r selected from the group consisting of dipyridyl andalkyldipyridyl, and recycled to the catalyst.

8. A process as claimed in claim 2 wherein the alkyl group is a methylgroup in the 4-position of the pyridine ring.

References Cited by the Examiner UNITED STATES PATENTS 3,053,846 9/62Varcoe 260296 4 OTHER REFERENCES Bond; Catalysis by Metals, pp. 407-409(Academic Press) (1962).

Lohse: Catalytic Chemistry, pp. 149-169, 204-211 5 (Chemical PublishingCo.) (1945).

WALTER A. MODANCE, Primary Examiner.

JOHN D. RANDOLPH, Examiner.

1. AN IMPROVED PROCESS FOR THE MANUFACTURE OF 2:2''DIPYRIDYL AND ALKYLDERIVATIVES THEREOF FROM A FIRST MEMBER SELECTED FROM THE GROUPCONSISTING OF PYRIDINE AND AN ALKYLPYRIDINE BY HEATING SAID FIRST MEMBERAT A TEMPERATURE ABOVE 100*C. WITH CATALYST CONTAINING A SECOND MEMBERSELECTED FROM THE GROUP CONSISTING OF RHODIUM, OSMIUM AND IRIDIUM INFINELY DIVIDED FORM.